Spin bowl compatible polyamic acids/imides as wet developable polymer binders for anti-reflective coatings

ABSTRACT

Anti-reflective compositions and methods of using these compositions to form circuits are provided. The compositions comprise a polymer dissolved or dispersed in a solvent system. In a preferred embodiment the polymers of the composition include recurring monomers having the formulas 
                         
where: (1) each R is individually selected from the group consisting of hydrogen, —OH, aliphatics, and phenyls; and (2) L is selected from the group consisting of —SO 2 — and —CR′ 2 —, where each R′ is individually selected from the group consisting of hydrogen, aliphatics, phenyls, and —CX 3 , where each X is individually selected from the group consisting of the halogens. The resulting compositions are spin bowl compatible (i.e., they do not crosslink prior to the bake stages of the microlithographic processes or during storage at room temperature), are wet developable, and have superior optical properties.

RELATED APPLICATIONS

This application claims the priority benefit of a provisionalapplication entitled SPIN BOWL COMPATIBLE POLYAMIC ACIDS/IMIDES AS WETDEVELOPABLE POLYMER BINDERS FOR BARCS, Ser. No. 60/349,569, filed Jan.17, 2002, incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is concerned with new polymers and anti-reflectivecompositions for use in the manufacture of microelectronic devices.These compositions include a polyamic acid and are developable inaqueous photoresist developers.

2. Description of the Prior Art

Integrated circuit manufacturers are consistently seeking to maximizesubstrate wafer sizes and minimize device feature dimensions in order toimprove yield, reduce unit case, and increase on-chip computing power.Device feature sizes on silicon or other chips are now submicron in sizewith the advent of advanced deep ultraviolet (DUV) microlithographicprocesses.

However, a frequent problem encountered by photoresists during themanufacture of semiconductor devices is that activating radiation isreflected back into the photoresist by the substrate on which it issupported. Such reflectivity tends to cause blurred patterns whichdegrade the resolution of the photoresist. Degradation of the image inthe processed photoresist is particularly problematic when the substrateis non-planar and/or highly reflective. One approach to address thisproblem is the use of an anti-reflective coating applied to thesubstrate beneath the photoresist layer. While anti-reflective coatingsare effective at preventing or minimizing reflection, their use requiresan additional break-through step in the process in order to remove thecoatings. This necessarily results in an increased process cost.

One solution to this problem has been the use of wet developableanti-reflective coatings. These types of coating can be removed alongwith the exposed areas of the photoresist material. That is, after thephotoresist layer is exposed to light through a patterned mask, theexposed areas of the photoresist are wet developable and aresubsequently removed with an aqueous developer to leave behind thedesired trench and hole pattern. Wet developable anti-reflectivecoatings are removed during this developing step, thus eliminating theneed for an additional removal step. Unfortunately, wet developableanti-reflective coatings have not seen widespread use due to the factthat they must also exhibit good spin bowl compatibility and superioroptical properties to be useful as an anti-reflective coating. Thus,there is a need for anti-reflective coating compositions which areremoved by conventional photoresist developers while simultaneouslyexhibiting good coating and optical properties.

SUMMARY OF THE INVENTION

The present invention broadly comprises microlithographic compositions(and particularly anti-reflective coating compositions) that are usefulin the manufacture of microelectronic devices.

In more detail, the compositions comprise a polymer dispersed ordissolved in a solvent system. In one embodiment, the preferred polymersare polyamic acids. The polyamic acids preferably include recurringmonomers having the formulas

-   -   where each of

-   -    individually represent an aryl or aliphatic group.

In this embodiment, the polyamic acids are preferably formed bypolymerizing a dianhydride with a diamine. Preferred dianhydrides havethe formula

-   -   where

-   -    represents an aryl or aliphatic group.

Particularly preferred dianhydrides are:

Preferred diamines have the formula

-   -   where

-   -    represents an arly or aliphatic group.

Particularly preferred diamines are:

-   -   X=O, S, —CH₂, —C(CH₃)₂, or —C(CF₃)₂,        H₂N—(CH₂)_(n)—NH₂    -   n=2-8,

In another preferred embodiment, the preferred polymers includerecurring monomers having the formulas

In the foregoing formulas, each R is individually selected from thegroup consisting of hydrogen, —OH, aliphatics, and phenyls. Preferredaliphatics are C₁-C₈ branched and unbranched alkyl groups such ast-butyl and isopropyl groups.

L is selected from the group consisting of —SO₂— and —CR′₂—. When L is—CR′₂—, then each R′ is individually selected from the group consistingof hydrogen, aliphatics (preferably C₁-C₈ branched and unbranchedalkyls), and phenyls, and —CX₃. In embodiments where R′ is —CX₃, each Xis individually selected from the group consisting of the halogens, withfluorine and chlorine being the most preferred halogens.

In yet another embodiment, the polymers are formed by polymerizing acompound having the formula

-   -   with a compound having the formula

In the formulas of this embodiment, each R is individually selected fromthe group consisting of —OH, —NH₂, hydrogen, aliphatics, and phenyls.Again, as with the first embodiment, preferred aliphatics are C₁-C₈branched and unbranched alkyl groups such as t-butyl and isopropylgroups. Furthermore, it is preferred that at least one R on each ring of(I) be —NH₂.

L is preferably selected from the group consisting of —SO₂— and —CR′₂—,where each R′ is individually selected from the group consisting ofhydrogen, aliphatics (preferably C₁-C₈ branched and unbranched alkylgroups), phenyls, and —CX₃. When L is —CX₃, each X is individuallyselected from the group consisting of the halogens.

Regardless of the embodiment, the compositions are formed by simplydispersing or dissolving the polymers in a suitable solvent system,preferably at ambient conditions and for a sufficient amount of time toform a substantially homogeneous dispersion. The polymer should bepresent in the composition at a level of 1-100% by weight, morepreferably from about 20-80% by weight, and more preferably from about40-60% by weight, based upon the total weight of solids in thecomposition taken as 100% by weight. The weight average molecular weightof this polymer is preferably from about 2,000-1,000,000 Daltons, morepreferably from about 5,000-500,000 Daltons, and even more preferablyfrom about 10,000-100,000 Daltons.

Preferred solvent systems include a solvent selected from the groupconsisting of propylene glycol methyl ether acetate (PGMEA), propyleneglycol methyl ether (PGME), and mixtures thereof. The solvent systemshould have a boiling point of from about 50-250° C., and morepreferably from about 150-200° C., and should be utilized at a level offrom about 50-99% by weight, and preferably from about 90-98% by weight,based upon the total weight of the solids in the composition taken as100% by weight.

Any other ingredients should be dissolved or dispersed in the solventsystem along with the polymer. One such ingredient is a crosslinkingagent. Preferred crosslinking agents include aminoplasts (e.g.,POWDERLINK® 174, Cymel® products) and epoxies. The crosslinking agentshould be present in the composition at a level of from about 0-50% byweight, and preferably from about 10-20% by weight, based upon the totalweight of the solids in the composition taken as 100% by weight. Thus,the compositions of the invention should crosslink at a temperature offrom about 100-250° C., and more preferably from about 150-200° C.

It is preferred that the compositions also include a light attenuatingcompound or chromophore. The light attenuating compound should bepresent in the composition at a level of from about 0-50% by weight, andpreferably from about 15-30% by weight, based upon the total weight ofsolids in the composition taken as 100% by weight. The light attenuatingcompound should be selected based upon the wavelength at which thecompositions will be processed. Thus, at wavelengths of 248 nm,preferred light attenuating compounds include napthalenes andanthracenes, with 3,7-dihydroxy-2-napthoic acid being particularlypreferred. At wavelengths of 365 nm, preferred light attenuatingcompounds include diazo dyes and highly conjugated phenolic dyes. Atwavelengths of 193 nm, preferred light attenuating compounds includecompounds containing phenyl rings.

It will be appreciated that a number of other optional ingredients canbe included in the compositions as well. Typical optional ingredientsinclude surfactants, catalysts, and adhesion promoters.

The method of applying the inventive compositions to a substrate simplycomprises applying a quantity of a composition hereof to the substratesurface by any known application method (including spin-coating). Thesubstrate can be any conventional chip (e.g., silicon wafer) or an ionimplant layer.

After the desired coverage is achieved, the resulting layer should beheated to induce crosslinking (e.g., to a temperature of from about100-250° C.). At a film thickness of about 40 nm and a wavelength ofabout 248 nm, the cured layers will have a k value (i.e., the imaginarycomponent of the complex index of refraction) of at least about 0.3, andpreferably at least about 0.45, and an n value (i.e., the real componentof the complex index of refraction) of at least about 1.0, andpreferably at least about 1.8. That is, a cured layer formed from theinventive composition will absorb at least about 90%, and preferably atleast about 99% of light at a wavelength of about 248 nm. This abilityto absorb light at DUV wavelengths is a particularly useful advantage ofthe inventive compositions.

A photoresist can then be applied to the cured material, followed byexposing, developing, and etching of the photoresist. Following themethods of the invention will yield precursor structures which have theforegoing desirable properties.

It will further be appreciated that the cured inventive composition iswet developable. That is, the cured composition can be removed withconventional aqueous developers such as tetramethyl ammonium hydroxideor potassium hydroxide developers. At least about 90%, and preferably atleast about 98% of the inventive coatings will be removed by a basedeveloper such as a tetramethyl ammonium hydroxide developer (e.g.,OPD262, available from Olin Photodeveloper). This percent solubility incommercially-available developers is a significant advantage over theprior art as this shortens the manufacturing process and makes it lesscostly.

Finally, in addition to the many advantages described above, the presentcomposition is spin bowl compatible. This is determined as described inExample 2, using PGMEA as the solvent and taking five measurements todetermine the average thicknesses. The percent solubility is calculatedas follows:

${\%\mspace{14mu}{solubility}} = {\quad{\left\lbrack \frac{\begin{matrix}\left( {{{{ave}.\mspace{11mu}{initial}}\mspace{14mu}{sample}\mspace{14mu}{thickness}} -} \right. \\\left. {{{ave}.\mspace{11mu}{final}}\mspace{14mu}{sample}\mspace{14mu}{thickness}} \right)\end{matrix}}{\left( {{initial}\mspace{14mu}{sample}\mspace{14mu}{thickness}} \right)} \right\rbrack*100.}}$The inventive compositions show a percent solubility of at least about50%, and more preferably at least about 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Scanning Electron Micrograph (SEM) depicting across-sectional view of a circuit structure showing how a wetdevelopable anti-reflective layer is removed when the photoresist isdeveloped;

FIG. 2 is an SEM of a cross-section of a circuit structure showing how aconventional thermosetting anti-reflective layer remains when thephotoresist is developed; and

FIG. 3 an SEM depicting a cross-sectional view of a circuit structureshowing how a wet developable anti-reflective layer according to theinvention is removed when the photoresist is developed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

The following examples set forth preferred methods in accordance withthe invention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Example 1 Preparation of Anti-Reflective Coating Composition

1. Polymer Preparation

A polyamic acid was produced by combining 4,4′-diaminodiphenyl sulfone(4,4′-DPS), 3,3′-dihydroxybenzidene (HAB), and4,4′-hexafluoroisopropylidene dipthalic anhydride (6FDA) (each obtainedfrom KrisKev Corporation) at a molar ratio of 0.46:0.46:1. Theseingredients were combined at 60° C. in diacetone alcohol (obtained fromAldrich). The mixture was stirred overnight and resulted in a darkbrown, viscous liquid having a solids content of 10% by weight.

2. Anti-Reflective Coating Preparation

The ingredients of Table 1 were mixed to yield an anti-reflectivecoating composition.

TABLE 1 Formulation I Percentage By Weight^(a) Polymer from Part 1 ofthis Example 1.58% PGMEA^(b) 48.50% Diacetone alcohol 48.5%3,7-dihydroxy-2-napthoic acid 0.95% Crosslinking Agent^(c) 0.47%^(a)Based upon the total weight of all ingredients in the compositiontaken as 100% by weight. ^(b)propylene glycol monomethyl ether acetate.^(c)MY720, a tetra functional epoxy resin available from Araldite;diluted 50% by weight in diacetone alcohol

TABLE 2 Formulation II Percentage By Weight Polymer from Part 1 of thisExample 1.23% PGMEA 48.80% Diacetone alcohol 48.8%37-dihydroxy-2-napthoic acid 0.74% Crosslinking Agent 0.43%

TABLE 3 Formulation III Percentage By Weight Polymer from Part 1 of thisExample 1.20% PGMEA 48.50% Diacetone alcohol 48.5%3,7-dihydroxy-2-napthoic acid 0.72% Crosslinking Agent 0.48%

TABLE 4 Formulation IV Percentage By Weight Polymer from Part 1 of thisExample 2.25% PGMEA 47.75% Diacetone alcohol 47.75%3,7-dihydroxy-2-napthoic acid 1.35% Crosslinking Agent 0.90%

Example 2 Testing Methods and Results

1. GPC Analysis

The polymers prepared in Part 1 of this example were analyzed todetermine molecular weight using HPLC with an attached gel permeationcolumn where n-methyl pyrillidone with tetrahydrofuran were used as themobile phase. The polymer prepared in Part 1 of Example 1 had amolecular weight of 24,908 and a molecular number of 13,462.

2. Spin Bowl/Solvent Compatibility Test

Each of the four formulations prepared in Part 2 of Example 1 wassubjected to a spin bowl/solvent compatibility test. This test wascarried out by spin-coating the composition onto five 4″ silicon wafersfor each sample. After spin-coating, the resulting layer was allowed todry for 24 hours at ambient conditions. At that time, the averageinitial film thickness on each wafer was determined using a Stokesellipsometer. After determining the thicknesses, each wafer was soakedwith a different solvent (acetone, ethyl lactate, PGMEA, propyleneglycol monomethyl ether (PGME), and 2-heptanone) for 180 seconds,followed by spin drying at 3500 rpm. The respective average final filmthicknesses were then remeasured using a Stokes ellipsometer. The finalthickness measurements of the samples showed that 100% of theanti-reflective coating layers had been removed for each solvent.

3. Film Stripping Test

Each of the anti-reflective coating compositions prepared in Part 2 ofExample 1 were subjected to a film stripping test to determine theamount of interaction between typical photoresist solvents and theunderlying anti-reflective coating layer. In this test, a 4″ siliconwafer was coated with the particular anti-reflective coating formulationfollowed by baking at 130° C. for 30 seconds and a second bake at 150°C. for 60 seconds. The film thickness was then measured using a Stokesellipsometer. After measuring the thickness, the wafer was sprayed withethyl lactate. The resulting puddle was allowed to stand on the waferfor 10 seconds followed by spin-drying of the wafer at 3500 rpm for 20seconds. The wafer was then remeasured with a Stokes ellipsometer todetermine the film thickness. The amount of stripping is the differencebetween the initial and final film thickness measurements. The percentstripping is

${\%\mspace{14mu}{stripping}} = {\left( \frac{{amount}\mspace{14mu}{of}\mspace{14mu}{stripping}}{{initial}\mspace{14mu}{average}\mspace{14mu}{film}\mspace{14mu}{thickness}} \right) \times 100.}$Compositions according to the invention will give a percent stripping ofless than about 20%, and preferably less than about 5%. Each of theseformulations exhibited no stripping at bake temperatures of 150-205° C.4. V.A.S.E. Measurements

In this procedure, 4″ silicon wafers were individually coated with eachof the formulations from Part 2 of Example 1. The respective refractiveindices (i.e., n value) and imaginary refractive indices (i.e., k value)were determined using variable angle spectrophotometric ellipsometery.Each formulation showed an n value of 1.1 and a k value of 0.45 at 248nm.

5. Photolithography

The formulations of Part 2 of Example 1 were spin-coated onto respective8″ silicon substrate at 3500 rpm for 60 seconds, yielding a film havinga thickness of 40 nm. The films were then baked at 130° C. for 30seconds, followed by 175° C. bake for 60 seconds. A commerciallyavailable, 500 nm photoresist (SEPR430, available from Shmetsu) wasspin-coated on each anti-reflective coating layer followed by a softbake at 90° C. The photoresist was then patterned with lines and spacesusing an ASML 5500/300 stepper with NANA of 0.63 and annularillumination with outer sigma of 0.87 and inner sigma of 0.57. After aKrF excimer laser exposure of 26 mj/cm², the photoresist was baked at110° C. for 90 seconds. The photoresist and the anti-reflective coatinglayer were then developed using a 0.26 N tetramethyl ammonium hydroxideaqueous developer (available under the name OPD262). A cross-sectionalview of one of the sample wafers is shown in FIG. 3.

1. In a composition for use in photolithographic processes wherein thecomposition comprises a polymer dissolved or dispersed in a solventsystem, the improvement being that said composition comprises acrosslinking agent and said polymer comprises recurring monomers havingthe formulas

wherein: each R is individually selected from the group consisting ofhydrogen, —OH, aliphatics, and phenyls; and L is selected from the groupconsisting of —SO₂— and —CR′₂—, where each R′ is individually selectedfrom the group consisting of hydrogen, aliphatics, phenyls, and —CX₃,where each X is individually selected from the group consisting of thehalogens.
 2. The polymer of claim 1, wherein at least one R on each ringis —OH.
 3. The polymer of claim 1, wherein L is —SO₂—.
 4. The polymer ofclaim 1, wherein L is —CR′₂—.
 5. The combination of: a substrate havinga surface; and an anti-reflective layer adjacent said surface, saidanti-reflective layer being formed from a composition comprising apolymer dissolved or dispersed in a solvent system, said polymercomprising recurring monomers having the formulas

wherein: each R is individually selected from the group consisting ofhydrogen, —OH, aliphatics, and phenyls; and L is selected from the groupconsisting of —SO₂— and —CR′₂—, where each R′ is individually selectedfrom the group consisting of hydrogen, aliphatics, phenyls, and —CX₃,where each X is individually selected from the group consisting of thehalogens.
 6. The combination of claim 5, said layer being a cured layer.7. The combination of claim 6, said cured layer being wet developable.8. The combination of claim 6, wherein said cured layer has a percentsolubility of at least about 50% when propylene glycol methyl etheracetate is the solvent.
 9. The combination of claim 5, wherein saidsubstrate is selected from the group consisting of silicon wafers andion implant layers.
 10. The combination of claim 6, said combinationfurther comprising a photoresist layer adjacent said cured layer. 11.The combination of claim 6, said cured layer being at least about 90%soluble in a base developer.
 12. The combination of claim 5, wherein atleast one R on each ring is —OH.
 13. The combination of claim 5, whereinL is —SO₂—.
 14. The combination of claim 5, wherein L is —CR′₂—.
 15. Thecombination of claim 14, where each R′ is —CF₃.
 16. A method of using acomposition in photolithographic processes, said method comprising thestep of applying a quantity of a composition to a substrate to form alayer thereon, said composition comprising a polymer dissolved ordispersed in a solvent system, said composition comprising acrosslinking agent, said polymer comprising recurring monomers havingthe formulas

wherein: each R is individually selected from the group consisting ofhydrogen, —OH, aliphatics, and phenyls; and L is selected from the groupconsisting of SO₂and —CR′₂—, where each R′ is individually selected fromthe group consisting of hydrogen, aliphatics, phenyls, and —CX₃, whereeach X is individually selected from the group consisting of thehalogens.
 17. The method of claim 16, wherein said applying stepcomprises spin-coating said composition onto said substrate surface. 18.The method of claim 16, wherein said substrate has a hole formedtherein, said hole being defined by a bottom wall and sidewalls, andsaid applying step comprises applying said composition to at least aportion of said bottom wall and sidewalls.
 19. The method of claim 16,further including the step of baking said layer, after said applyingstep, at a temperature of from about 100-250° C. to yield a cured layer.20. The method of claim 19, further including the step of applying aphotoresist to said cured layer.
 21. The method of claim 20, furtheringincluding the steps of: exposing at least a portion of said photoresistto activating radiation; and developing said exposed photoresist. 22.The method of claim 21, wherein said developing step results in theremoval of said cured layer from areas adjacent said exposedphotoresist.
 23. The method of claim 16, wherein said substratecomprises an ion implant layer.